It’s not always as great as you may think. My Mom and I lived for each other after my Dad died almost 25 years ago. It was painful to watch her deteriorate in the last year of her life as she struggled to stay alive because she worried about me. Part of loving someone is to do the best you can for them, then let them go to live their own life (possibly with their own children).
The fact that you have to ask for justification for abandoning your father shows that you’re not emotionally mature enough to make the decision yourself. I hate to be harsh, but if you’re old enough to have served in the military, you’re old enough to move on to a new life without your father.
Quit relying on others like your sister(s) and especially strangers on a forum to help you make decisions. You obviously love your father and in his own way he loves you, but move on with your life and if he contacts you (probably through your sister), reverse the roles of the Prodigal Son and welcome him back into your life if you’re truly ready.